Perceiving and mentally representing the locations of objects and places in one's immediate environment is a fundamental prerequisite to most of human behavior. Because locations can be specified only in and through a reference system, the scientific investigation of the reference systems used in perception and memory has become an extremely important area of contemporary research in spatial cognition. In the last decade, several lines of research have converged to suggest the importance of egocentric reference systems (i.e., those that code locations relative to the observer, such that places are linked to the organization of the body). Egocentric reference systems are particularly influential when people remember the locations of different objects in their immediate environment. Given the importance of egocentric reference systems in memories of object layouts, it is surprising that existing research has done little to understand more precisely the nature of this coding system. In particular, it is unknown which among three possible bases for an egocentric reference system (retina-based, head-based, and body-based) dominates spatial coding in memory. This research will examine this issue more closely, determining both the dominant bases for egocentric coding and the degree to which the influences of various egocentric reference systems are altered by the nature of the learning and testing environments. Completion of the project will lead to a clearer understanding of how humans encode spatial information in memory. This basic research will have immediate implications for computational models of spatial cognition as well as offering insight into the degree to which populations that do not have access to the sensory bases for certain reference systems (such as the blind and paraplegic) may productively use other systems in order to remember spatial information. Findings may also lead to ways of improving spatial abilities in the general population.